River estuaries a source of ‘blue’ power

Could the confluence of salt and fresh water be harnessed as a massive battery?

Millions of litres of water constantly flow into the sea from the world’s rivers yet scientists may have discovered a way of turning it into electricity without using barrages or even turbines.

A report on the New Scientist website states that a gigawatt of electricity could be created (enough to power 650,000 homes) by channeling the salt water of the north sea and the fresh water of the River Rhine through a type of battery.

The idea originates from the invention of the modern desalination plant that turns salt water into fresh water by pumping it through a membrane – a technique known as reverse osmosis.

One of the two inventors, Sidney Loeb, envisaged using the same technique to create pressurized water containing enough energy to power a turbine. Loeb named this process pressure retarded osmosis (PRO) and patented it in 1973.

The technology has been held back by the lack of a suitable membrane that divides the salt from the fresh, yet allows the molecules through when pressurized.

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